1. Field of the Invention
The present invention relates to a carburetion type burning apparatus for evaporating liquid fuel such as kerosene for burning.
2. Description of Prior Art
A conventional carburetion type burning apparatus will be described with reference to FIG. 5.
In FIG. 5, reference numeral 1 designates a fuel tank, and numeral 2 designates an electromagnetic pump for feeding kerosene contained in the fuel tank 1 into a carburetion chamber 4 in a carburetor 3 through a fuel pipe 18. Numeral 5 designates a carburetion stabilizing substance provided in the carburetion chamber 4. Numeral 6 designates a heater which maintains the temperature in the carburetion chamber 4 constant during the burning operation with the aid of a thermister 7 attached to a side wall of the carburetor 3 and a control circuit (not shown). A nozzle orifice 8 is formed above the carburetion chamber 4. A burner 9 is provided facing the nozzle orifice 8. There are arranged on or above the burner an ignition plug 10 for igniting the fuel gas and a flame rod 11 to detect an ion current in the flames.
Reference numeral 12 designates a needle having a sharp point for opening and closing the nozzle orifice. Numeral 13 is a movable piece formed integrally with the needle 12. Numeral 14 designates a solenoid which causes a sliding movement of the movable piece 13. Numeral 15 designates a spring for urging the movable piece 13 toward the right in the drawing to open the nozzle orifice 8 when the solenoid 14 is not actuated. Numeral 16 designates a return valve attached integrally with the movable piece 13 to prevent the kerosene from flowing into a pipe 17 which is in communication with the fuel tank 1 when the nozzle orifice 8 is opened.
The movable piece 13 is moved toward the left in the drawing against the spring 15 when solenoid 14 is actuated to securely close the nozzle orifice 8 with the needle 12, and the return valve 16 is opened to recover the kerosene remaining in the carburetion chamber 4 which flows into the fuel tank 1 through the pipe 17.
The operation of a conventional burning apparatus will be described with reference to the time chart in FIG. 6.
When an operation switch (not shown) is turned on, the carburetor 3, the carburetion chamber 4 and the carburetion stabilizing substance 5 are heated by the heater 6 so that the carburetion chamber 4 is preheated at a predetermined temperature (250.degree. C.-300.degree. C.) which is required to evaporate the kerosene. Since the kerosene deposited in the carburetion chamber 4 is partially evaporated in this preheating period, a bad smell is produced from the nozzle orifice 8. To avoid the smell, the nozzle orifice 8 is closed with the needle 12 by actuating the solenoid 14. Upon completion of the preheating operation when the temperature of the carburetion chamber 4 reaches the predetermined level, the electromagnetic pump 2 is actuated, and kerosene is supplied from the fuel tank 1 through the pipe 18 to the carburetion chamber 4 where it is heated to become fuel gas.
At that moment, current to the solenoid 14 is stopped and the needle 12 is slidingly moved to open the nozzle orifice 8, whereby the fuel gas is ejected through the nozzle orifice 8. In this case, air for combustion is sucked from the environment of the nozzle to make a gas mixture. The gas mixture is then introduced in the burner 9. An ignition plug 10 mounted on the burner 9 produces an electric discharge at the same time as the completion of the preheating period. The gas mixture is ignited by a spark in the electric discharge. After ignition, an ion current in the flames is detected by the flame rod 11. When the ion current reaches a predetermined level or higher, the discharge of the ignition plug is stopped by a control circuit (not shown).
In the burning operation, the heater 6 is controlled so that the temperature in the carburetion chamber 4 is maintained at a constant level by the aid of the thermister 7 and the control circuit, so that warm air is supplied to a room by the operation of a well-known convection fan (not shown).
When the burning operation is to be stopped, the operation switch is turned off. Then, the electromagnetic pump 2 is stopped to stop the supply of kerosene. At the same time, the solenoid 14 is actuated by a current to close the nozzle orifice 8 with the needle 12. Then, the return valve is opened so that the fuel gas remaining in the carburetion chamber 4 condenses while it passes through the space around the needle 12 and the movble piece 13. The liquid fuel thus produced is recovered in the fuel tank 1 through the pipe 17.
Current to the heater 6 is also stopped at this time. Accordingly, the temperature in the carburetion chamber 4 decreases and the fuel gas remaining in the chamber becomes liquid.
When the nozzle orifice 8 is opened by deenergizing the solenoid 14 after a time period sufficient to reduce the temperature of the carburetion chamber 4, there is only a small amount of fuel gas remaining in the carburetion chamber 4. Therefore, the leakage of fuel gas, which causes a bad smell, from the nozzle orifice 8 is prevented. The convection fan is also stopped at the same time that the fire is extinguished.
In a conventional carburetion type burning apparatus having the construction as abovementioned, the nozzle orifice 8 is closed when the fuel gas fills the carburetion chamber 4 and the fire is extinguished. Accordingly, the fuel gas is condensed into liquid fuel causing a large amount of kerosene to remain in the carburetion chamber 4 and to be recovered in the fuel tank 1 through the pipe 17.
As is well-known, kerosene heated at a high temperature is easily oxidized and easily produces tar (carbide), whereby a large amount of tar deposits and accumulates on the inner wall of the carburetion chamber 4 and on the carburetion stabilizing substance 5. As the deposition of the tar increases, the carburetion of the kerosene is hindered causing a deterioration of the burning condition.